Numerous approaches to the separation of a gas from a mixture of gases by differential permeation have been investigated. Robb et al., in U.S. Pat. No. 3,335,545, have proposed use of a liquid, entrapped in a porous or permeable support, to separate mixtures of gases. The use of a so-called "quasi-liquid film," for example, diethylene glycol, in a support has permitted separation of carbon dioxide from nitrogen, hydrogen or oxygen, the selectivity being somewhat higher than would be predicted on the basis of the molecular weights of the gases as the sole factor, influencing separation. Ward, III, has proposed, in U.S. Pat. No. 3,503,186, a similar procedure for separating sulfur dioxide from other gases.
The use of facilitated transport liquid membranes has been reviewed by Way et al., J. Membrane Science, vol. 12 (1982), pages 239-259. Another typical disclosure of gas separation using a facilitated transport immobilized liquid membrane is that of Bassett et al., Biochimica et Biophysica Acta, vol. 211 (1970), pages 194-215. Facilitated transport of gases through liquid membranes is also recited, for example, in the following U.S. Patents:
U.S. Pat. No. 3,396,510, Ward, III, et al. PA1 U.S. Pat. No. 3,676,220, Ward, III PA1 U.S. Pat. No. 3,819,806, Ward, III, et al. PA1 U.S. Pat. No. 4,014,665, Steigelmann PA1 U.S. Pat. No. 4,015,955, Steigelmann et al. PA1 U.S. Pat. No. 4,119,408, Matson PA1 U.S. Pat. No. 4,147,754, Ward, III PA1 U.S. Pat. No. 4,174,374, Matson PA1 U.S. Pat. No. 3,400,054, Ruka et al. PA1 U.S. Pat. No. 3,432,363, Gillis PA1 U.S. Pat. No. 3,527,618, Bushnell PA1 U.S. Pat. No. 3,727,058, Schrey PA1 U.S. Pat. No. 4,317,865, Trocciola et al. PA1 U.S. Pat. No. 4,330,633/U.K. 2,082,156, Yoshisato et al.
Ward, III, et al. '510 recite using an immobilized liquid film as a permeable membrane, wherein the liquid film contains at least one soluble, non-volatile, dissolved carrier species, which is reversibly chemically reactive with a selected component of a gaseous mixture.
Kimura et al. (U.S. Pat. No. 4,318,714) have recited using an ion-exchange membrane to accomplish facilitated separation of a gas from a mixture of gases.
Yamamoto et al. (U.S. Pat. No. 3,155,467) have disclosed separation and purification of hydrogen, using a palladium alloy as a permeable wall structure.
Solid and molten salt electrolytes have been disclosed, in the fuel cell or electrochemical arts, in the following representative patents:
Yoshisato et al., in U.S. Pat. No. 4,330,633, recite using a solid electrolyte comprising a sintered body of mixed inorganic metal oxides as a membrane for the regeneration of oxygen at relatively high temperatures (about 800.degree. C.).
Oxygen is known to permeate selectively through metallic silver. However, oxygen fluxes at reasonable temperatures (about 400.degree. C.) are low, as reported by Gryaznov et al., Russian. J. Phys. Chem., vol. 47 (1973), pages 1517-1519. At higher temperatures, metallic membranes for the separation of oxygen from other gases are unstable, see Mulhaupt, U.S. Pat. No. 3,359,705.
A limiting feature in many of these disclosures is that a gas should not completely permeate the electrolyte or electrode, since complete penetration could short circuit the device.
Batigne et al., U.S. Pat. No. 4,396,572, recite using a porous ceramic barrier, having a plurality of superimposed layers of pastes of varying composition, to separate uranium hexafluoride isotopes by ultrafiltration.
It is apparent that presently available membranes for separation of gases by conventional diffusion, permeation or ultrafiltration methods have low permeation rates, are relatively unselective or are complex in structure.
It is therefore an object of this invention to provide methods and articles for the separation of gases from mixtures, which have higher permeation rates and much higher selectivity than presently available methods and membranes and which are also more simple to construct and to use.